Industrial process control systems are used to control a variety of manufacturing and processing systems. To be effective, process control systems must be capable of operating reliably under a wide range of extreme and often hostile environments both in terms of physical as well as electromagnetic conditions.
Modern process control systems often comprise a variety of smart devices, such as control valves, pressure and temperature sensors and flow meters. Smart devices are generally considered to be those that include CPUs and which are therefore capable of processing control or measured information, e.g., from a sensor.
Fieldbus is a two wire, bidirectional digital communication arrangement that interconnects smart field devices to each other, to control systems and/or to instruments located in a control room. References herein to a Fieldbus refer to a bus operating according to a Fieldbus protocol. The Fieldbus communications protocol is described in FIELDBUS FOUNDATION.TM., Fieldbus Specification, Function Block Application Process, Parts 1 and 2, Revision PS 1.0, Apr. 27, 1995 which is hereby expressly incorporated by reference. It should be noted that while the cited Fieldbus Specification documents are useful in providing an understanding of the Fieldbus protocol, they are not prior art to the present application.
The Fieldbus digital communications protocol allows communication among a variety of smart devices, such as transmitters, valves, local controllers, sensors, etc. The Fieldbus protocol, which uses digital signals to communicate control information and data between networked devices, offers several advantages in terms of reliability and connectivity over the older 4-20 mA analog communications protocol previously used to network control system devices and sensors together.
In order to monitor or control devices coupled together by a Fieldbus as part of a network, it is often desirable to be able access the network at a convenient site, e.g., in the field near a sensor or control valve.
Accordingly, there is a need for a portable unit which can be easily attached to the Fieldbus of a control system, which can display Fieldbus information, and which can be used to monitor and program the various devices which comprise the control system.
Where a computer is used as part of the portable unit for monitoring and controlling devices attached to the Fieldbus of a control system, an interface device for coupling the computer to the Fieldbus is required. It is highly desirable that such an interface device be low in cost, easily portable, and be capable of reliably transmitting information over, and receiving data from, the Fieldbus.